Purified cellulose fiber has advantages such as excellent dimensional stability, high adhesiveness, and an elastic modulus that exhibits low temperature dependence (change of an elastic modulus according to the variation of temperature). The purified cellulose fiber is easily produced by passing a dissolved cellulose raw material through water, an alcohol, or an aqueous solution of water and an ionic liquid. The spinning of cellulose by using such an ionic liquid is reported in Patent Documents 1 and 2. It can be said that the process for producing purified cellulose fiber obtained by using the ionic liquid is a method that imposes a light load on the environment.
Generally, in a tire, the purified cellulose fiber is twisted, made into cords, and subjected to an adhesion treatment. Thereafter, the fiber is covered with rubber, and used in the form of a fiber-rubber complex. In a tire, fiber is used mainly for the purpose of reinforcing rubber. Accordingly, it is preferable for the fiber to have high toughness. The higher the toughness of the fiber, the more the amount of the fiber used in the tire can be reduced. As a result, the weight of the tire and the rolling resistance can be reduced.
Furthermore, if the amount of the fiber used can be reduced, the amount of materials and energy required for producing the tire can be reduced.